An exhaust system of an internal combustion engine can include a turbine wheel set in a turbine housing to create backpressure. In such a system, as pressurized exhaust gas from the internal combustion engine passes through the turbine housing (e.g., en route to an atmospheric outlet), the turbine wheel harnesses energy as the exhaust gas expands.
A turbocharger can include a variable nozzle turbine (VNT), which can include one or more types of mechanisms that can alter geometry of a passage or passages between an exhaust gas volute and a turbine wheel space. As an example, a VNT can control the flow of exhaust gas to a turbine wheel through use of vanes that can be moved to alter geometry of throats through which the exhaust gas can flow to the turbine wheel.
As an example, at low engine speed, vanes may be controlled to move them toward a closed orientation that can direct the flow of exhaust gas through smaller sized throats and, for example, in a particular tangential direction toward an inducer portion of a turbine wheel. Such an approach can increase turbine power and boost pressure at low engine speeds.
As an example, at higher engine speeds, vanes may be controlled to move them toward an open orientation that can direct the flow of gas through larger sized throats, which lessen restriction to flow compared to smaller sized throat associated with a more closed orientation. In a more open orientation of the vanes, exhaust gas flow may be maximized and directed in a particular tangential direction toward an inducer portion of a turbine wheel in a manner that helps to avoid turbo over-speed while maintaining a desired level of boost pressure for an internal combustion engine.